Method and apparatus for conditioning air



Aug. 31, 1937. R D W 2,091,353

METHOD AND APPARATUS FOR CONDITIONING AIR Original Filed May 23, 1933 2 Sheets-Sheet l 5 0000000000 Oooooooo OGOOOOOOOO HIS ATTORNEY5 zw lw Aug. 31, 1937. c. R. DOWNS 2,091,353.

METHOD AND APPARATUS FOR CONDITIONING AIR Original Filed May, 25, 1933 2 Shets-Shef 2 HI 5 ATTORNEYS Patented Aug. 31, 1937 UNITED STATES PATENT OFFICE Charles R. Downs, Old Greenwich, Coma, as-

Signor to Weiss and Downs, Inc., New York,

N. Y., a corporation of New York Original application May 23, 1933, Serial No.

Divided and this application October 28, 1935, Serial No. 47,039

4 Claims.

This invention relates to improvements in the art of controlling the moisture content of air or gases in enclosed spaces. One object of my invention is to provide an improved method and 5 improved apparatus to reduce the moisture content of air when this is too high to satisfy the requirements of comfort for living beings in enclosed spaces or the requirements of proper manufacture or storage of various materials. The

dehumidification of air is generally most essential in warm summer months and for many purposes reduction in the air temperature is not necessary or desirable. According to my invention, the air maybe dehumidified without temperature reduction.

Another object of my invention is to provide an apparatus which in addition to performing the above functions will also humidify air when this is required. Such humidification is normally desirable during the cold winter months.

By my process and apparatus, I am able to dehumidify air at a temperature considerably above its dew point. This I accomplish by employing a deliquescent solid and its water solution in a novel manner.

Briefly the general method of dehumidification which I employ comprises passing the air through a series of drying zones which include a, drying zone, or predrying step, wherein the deliquescent material is in its liquid phase, and a plurality of drying zones wherein the deliquescent material is in its solid phase. The air during its passage through this series of drying zones is cooled in order to remove the heat developed by the ab- 35 ior ptlion of the moisture by the deliquescent maeria According to one manner in which this method of air dehumidification may be carried out, the deliquescent solid, preferably calcium chloride, is

40 supported in a plurality" of separate masses or beds above a series of trays superposed one above the other in cascade relation. The air to be dried is directed over the surfaces of pools of the drying liquid which are maintained on these trays, and thence into successive contact with the separate masses of the solid drying material and the cooling means associated therewith. The solution is drained from each of the several beds of solid deliquescent material onto the uppermost 50 tray, and after the solution has passed down through the series of trays and becomes diluted to'such an extent that it will absorb substantially no further moisture, it is discharged to waste.

I have found by actual practice that upon long 5;, continued operation a tough foam blanket tends to form on the surfaces of the unsaturated solutions of calcium chloride comprising the pools. This gradually reduces the efficiency of moisture absorption in the predrying step or zone. Furthermore, and more important, is the fact that dust in being quantitatively removed from the air both by contact with the pools of calcium chloride solution and with the saturated, viscous solutions of calcium chloride on the surfaces of the solid calcium chloride, collects as a sludge in these pools and makes necessary intermittent cleaning.

These objectionable features I have eliminated by artificially causing the calcium chloride solution to be agitated and made to flow through the pools at a rate-that will keep them clear of foam blankets and sludge. To accomplish this, I may use a pump, whose function is completely described below, to recirculate the solution in the predrying step. It will be understood that without this recirculation the velocity of fiow of the solution through the pools on the respective trays is governed by the rate of moisture absorbed from the air, and consequently is extremely low, amounting to a mere dripping of the solution.

I moreover have found it desirable to cool the recirculated solution before it is discharged to the top tray of the superimposed s ries of trays since by doing so the top pool is made more viscous and at the same time possesses a lower vapor pressure than the pools below.

By recirculating a relatively large volume of cooled calcium chloride-solution in the predrying step, I form a curtain or cascade of the same as it discharges over the lips of the trays in flowing from tray to tray. This flow of solution may be subdivided into a multiplicity of small streams by suitable means and in so doing, I greatly increase the emciency of contact between the air to be dried and the calcium chloride solution. This increased contact area is not merely the area of the liquid cascade itself but due to the high speed of air through the apparatus liquid is entrained and is thrown against the vertical walls of the predrying section of the apparatus as well as the lower surfaces of thetrays. This morethan doubles the wetted surfaces of the apparatus. All of this is accomplished without increasing the resistance to airflow through the apparatus to any appreciable degree which is of great importance from the standpoint of blower capacity.

This improvement in process and apparatus for dehumidifying air moreover provides an improved structure and process for humidifying air. The pump provided for recirculating calcium chloride solution is used to recirculate heated water over the trays en cascade. The cooling means for cooling the recirculated calcium chloride solution during the dehumidification of air then becomes a heating means for heating the recirculated water for the humidification of air. This improvement moreover is more economical as only a very small part of the water fed to the apparatus for humidifying the air is wasted to the sewer,-

the volume so wasted being only sufficient to keep in solution the salts normally present in water and thereby prevent them from separating out on the surfaces of the heating means. Furthermore, the process and apparatus which I disclose herein is especially suitable for humidifying air in that it automatically heats air after it is humidified to a temperature that is always considerably above that of the air immediately after humidification.

Additional features of my invention will be apparent from a consideration of the accompanying drawings, in which two forms of apparatus for carrying out the invention are illustrated, and from consideration of the following detailed description of the invention in connection with these drawings. It will be understood, however, that the scope of my invention is defined in the appended claims.

In these drawings:

Fig. 1 is a vertical longitudinal section of one form of air conditioning apparatus of my invention.

Fig. 2 is a transverse vertical section taken along line 22 of Fig. 1. I

Fig. 3 is a longitudinal vertical section showing a modified form of apparatus.

Fig. 4 is a longitudinal vertical section showing another modified form of apparatus.

Referring now to the accompanying drawings, and first to Figs. 1 and 2, the form of apparatus here shown for carrying out the method of my invention comprises a housing I forming therein an air treating chamber. This housing is made in three superimposed sections, predrying or a tray section 2, a compartment section 3 and a bin section 4. These sections are made of sheet metal bound at the corners with suitable steel shapes to give stiffness. At the meeting edges of sections 2 and 3 and likewise 3 and 4, they are provided with angle bars having apertures for the reception of bolts 5 and 6 respectively by means, of which the sections are secured together.

By making the housing I in these sections it may be dismantled and carried through existing doorways even for apparatus of large capacity. Furthermore, this permits the compartment section 3 to be reversed end for end upon the predrying section 2 which may be of advantage in installing the treating chamber in a selected space. Moreover, where variations in calcium chloride storage capacity are desirable, higher or lower bin sections 4 may be bolted to the compartment section 3. The air inlet 1 into the space 8 receives air from an air distributing box 9 which extends horizontally along the wall of section 2. The air outlet from housing I is shown at In.

The liquid holding trays II are sealed in any convenient manner to the vertical walls of the section 2 along three edges and alternate trays are spaced from a fourth vertical wall by staggered passages to cause the air to flow in a zig zag fashion back and forth laterally across alternate trays during its progress up through the stack of trays in the direction of the arrows in Fig. 2. The trays II are provided at the edges adiacent these air passages with lips l2 to retain a pool of liquid on each tray and to reinforce the edges to prevent sagging. The space ii below the lowermost tray serves to collect the liquid as it leaves the lowermost tray and also as a space for receiving the incoming air. The fioor I5 is sealed toall four walls of section 2 and is provided with a drainage opening l3 through which liquid is discharged from space 8. This opening is surrounded by a lip [4 for maintaining a pool of liquid on floor l5.

In the installation of the apparatus, the housing I should be positioned in such a manner that the liquid holding trays, as well as the floor of the housing, are horizontal. Thus the liquid will be maintained on these trays at a uniform 'lepth and filling of the trays to capacity may be effected. In this manner the absorptive power of the liquid will be utilized to a greater extent and none of the same will be carried to the discharge prematurely.

Drainage opening l3 communicates with a liquid reservoir IS in which is immersed a heat exchanger or cooler I! of any suitable construction. An overflow pipe I8 is provided which may be connected with the sewer for discharge of waste liquid from the reservoir IS. The heat transferring coil l! is provided with an inlet I9 and an outlet I9a. A pump driven by motor 2| has its suction pipe 22 immersed in the liquid reservoir l6 below the level of the overflow pipe l8 and its discharge pipe 23 is connected through the wall of section 2 above the top tray l I. A branch pipe 24 is provided so that a part or all ,of the liquid discharged by the pump 20 may be carried from the system by adjusting the threeway cook 25.

When the air has passed over the trays II as described above, and reaches the space above the topmost tray its direction of flow is changed from crosswise flow to lengthwise flow. and to do this the compartment section 3 is provided with a bottom plate 26 which completely covers. the bottom of section 3 aside from the air passageway 21. The air is caused by this plate to flow towards this air passageway and is discharged into the compartment section 3 through this passageway.

In the compartment section 3 there are pro vided three compartments 28, 29 and 30 of progressively increasing linear dimensions each to contain a bed or moss of solid calcium chloride when the apparatus is-operating as a dehumidifying unit. A screen 3| is provided to support the leading face of the mass of solid calcium chloride resting in the first compartment 28. There are also provided two heat exchangers or air coolers 32 and 33 which also separate the compartments 28, 29 and 30.

The air entering compartment section 3 through passageway 21 passes successively through the screen 3|, the solid calcium chloride in compartment 28. the cooler 32, the solid calcium chloride in compartment 29, the radiator 33, the solid calcium chloride in compartment 30 and the screen 34, and leaves the apparatus through the outlet duct ll. The heat exchangers 32 and 33 may conveniently be made of finned tubing. These heat exchangers, when the apparatus is used as a dehumidifying unit. are for the purpose of cooling the air passing through them to remove the latent heat of condensation of moisture removed from the air together with the heat of solution of the calcium chloride to thereby control the temperature of the respective masses of solid calcium chloride in compartments 29 and 3B.

The successful and economical reduction of humidity throughout an enclosed space such as a dwelling house depends upon producing a com- 5 paratively small quantity of air having as low a relative humidity as possible, in order to avoid the necessity of circulating through the dehumidifying apparatus an unduly large volume of air. In accordance with one of the features of my present invention the production of air having the desired low humidity is aided by maintaining the final bed or mass of deliquescent solid through which the air passes, that is, bed

30, at an average temperature which is lower than the average temperature of the preceding bed, that is, bed 29. In fact it is desirable though not necessary, to maintain the several beds or masses of deliquescent solid 28, 29 and 30 at progressively lower average temperatures. It is moreover desirable to maintain the temperatures of all of the drying zones as low as practicable, and this is especially true of the liquid phase drying zone, since by so doing the liquid discharged to waste through overflow outlet I8 is at maximum dilution, or in other words contains a minimum of the deliquesced solid.

With these considerations in mind, heat exchangers 32 and 33 may be connected in parallel to the source of cooling water or other fluid which 30, is used for cooling them, and the rate ofv flow of such cooling fluid adjusted to allow the several masses or beds of deliquescent solid to assume during operation of the apparatus the desired relative temperature. It will be understood that 5 thermostatic control of this flow of the cooling fluid may be employed if desired.

Preferably, however, the heat exchangers 32 and 33 are so connected that the cooling water flows through them in series, the water first flowing through heat exchanger 33 and then through 32. This permits eflicient utilization of the cooling water and assists in controlling the temperature of the mass of calcium chloride in compartment at a lower point than that in compart- 45 ment 29. If a. larger number of compartments are to be used in series, I prefer connecting the heat exchangers associated withsuch a series in the above manner so that the cooling water flowing therethrough will aid in producing progressiv ely lower temperatures in the masses of calcium chloride in the consecutive compartments and the efiect of this is to approach the minimum possible quantity of moisture in the air before it is discharged fromthe outlet l0.

The heat exchangers 32 and 33 as above connected may be connected in parallel with the heat exchanger IT or in series therewith but I prefer to connect these heat exchangers in series as shown in Fig. 1, the cooling wateror other fluid flowing first through heat exchanger l1, then through heat exchanger 33, then through heat exchanger 32. It will be understood that the cooling water enters the heat exchanger'system by means of pipe l9 and leaves by outlet 35 of heat exchanger 32 from which it is discharged to waste or for further use.

The bottom plate 26 of compartmentsectionj l forms a collector plate for receiving'The concentrated calcium chloride solution which drips from the masses of solid calcium chloride in the compartments, 29 and 30 and this plate is provided with small perforations 36 to drain the solution to the body of liquid recirculated by pump 20. These several solutions are each saturated so that a slight reduction in temperature would cause them to resolidify. Such reduction in temperature is avoided, however, since the solutions are drained directly and separately onto the uppermost tray H. The solutions are thus prevented from coming in contact with the heat exchangers 32 and 33, and by discharging the solutions through the orifices 36 there is no opportunity for cooling to occur.

The solid calcium chloride shown in the compartments 28, 29 and 30 is in lump, briquet or generally spheroidal form and as these fragments liquefy and are reduced in size, the mass settles and contracts in volume. The bins 31, 38 and 39 of bin section 4 serve to automatically replenish the calcium chloride mass in the compartments. The bins are divided from each other within the bin section 4 by the division walls 40 and 4 I. for fresh calcium chloride lumps in bins 31, 38 and 39 approximating the rate at which the calcium chloride liquefies in the compartments 28, 29 and 30. These division walls Ml and M may be in a fixed position or may be attached to the tops of the radiators 32 and 33 by hinges with their upper edges free to be moved longitudinally to vary the ratio of these volumes. For" this purpose, sliding plates 42 and 43 are provided so that by adjustment of the top edges of the division walls they may be made to fit snugly against the under side of the cover 44 to prevent air from by-passing the heat exchangers 32 and 33.

Fixed slanting metal sheets 45 and 46 are provided to cause the masses of solid calcium chloride in the bins adjacent thereto to feed into compartments 28 and 30 but it is to be understood that these or similar sheets may beadjustable like the division walls 40 and 4| if desired. The cover 44 may be hinged at 41 or fastened to the top of the section 4' by any suitable means to make a tight fit.

In Figures 1 and 2 the slanting walls of the bins are shown in a slanting position longitudinally of the apparatus. It is to be understood, however, that they may also be slanted transversely to provide a still greater capacity for a given height.

As the masses in the compartments following the coolers shrink in volume, solid calcium chloride automatically feeds down from the'storage bins to keep these compartments full, thereby preventing air from by-passing the masses and at the same time utilizing the maximum eiiiciency of the heat exchanger surfaces at all times. The bins in themselves are highly advantageous in that they may be made of sufficient size to hold enough solid calcium chloride to last for considerable periods of time thereby permitting infrequent servicing of the apparatus.

Furthermore, the solid calcium chloride contained in a series of compartments liquefies most rapidly in the first compartment and progressively more slowly in the compartments following in the series. By the provision of storage bins, this unequal rate of use is compensated for by constructing the bins with varying volumes to suit the rates at which the calcium chloride is liquefied. For example, under certain circumstances with compartments of equal length, the ratio of the rate of liquefaction of the solid calcium chloride in the compartments where there are three in series may be, for example, 50%, 30% and 20% of the total solid calcium chloride therein. If the compartments are of the same horizontal cross sectional dimensions and the bin walls are vertical and in line with the By slanting these walls I provide storage sides of the compartments, the bin capacities should have relative volumes of 5, 3 and 2 if the bins are to be recharged with calcium chloride over the same time intervals. This makes the first bin in the series unduly high since the amount to be charged into this bin is one half the total.

Moreover, since the heights of cellar ceilings are limited in ordinary houses, the amount of calcium chloride that can be charged at a given time is therefore limited and frequency of charging unduly increased. This difliculty is overcome by slanting the bin walls at suitable angles to adjust the volumes to correspond more exactly with the rate at which the calcium chloride liquefies in the compartments. By this means, the distance to which the calcium chloride has to be lifted during charging is reduced and this constitutes an improvement except in cases where it may be desirable to charge the calcium chloride from an upper floor.

In addition to the above considerations, there is another reason why the compartments should be constructed with progressively increasing length, and the bins made with progressively decreasing capacity. If the calcium chloride in the compartments liquefies at the above rate, for examples 5, 3 and 2, and the compartments are all of equal length the compartment spaces are not all being efficiently utilized. For example, if the first compartment, which receives air containing the greatest content of water, is too long, the air passing therethrough becomes heated to such an extent during the removal of moisture in the front portion of the calcium chloride bed that substantially no moisture will be removed in the latter portion. Consequently very little calcium chloride will be liquefied in this latter portion and this represents wasted volume. On the other hand in the second compartment the air received has a lesser moisture content and neither the bed nor the air in the second compartment will be heated to such an extent as in the first compartment, so that the second compartment remains operative over a greater space, and consequently a smaller portion of the volume of calcium chloride therein is inefiective. The same thing is true of the third compartment. The third compartment has still less moisture to remove and none of the calcium chloride is ineffective. If the compartments are made with lengths of 2, 3 and 5 I still obtain liquefaction rates of 5, 3 and 2 but I obtain a lower exit air relative humidity from the third compartment than when the compartments under the same operating conditions are of equal length.

This increased efficiency in the same total contact length is probably due to the fact that I have eliminated useless bulk of calcium chloride earlier in the series and provided an increased bulk in the last compartment where it is available for a final clean-up of the moisture. I therefore have succeeded in producing a higher rate of moisture removal and a lowered moisture content of the exit air with a given volume of calcium chloride, constituting a great advantage in process and apparatus. There will then be about of the total calcium chloride liquefied in the first compartment whose volume is only 20% of the total volume of the compartments. The provision of bins of the proper volume gradations above such a series of compartments constitutes a valuable improvement for eiiicient servicing and operation. It is to be understood that the above ratios are not correct for all conditions of use but are acetate given merely as illustrative of the principle involved.

When the apparatus shown in Figs. 1 and 2 is used for humidifying air, as for example in the winter time, the masses of calcium chloride lumps are removed and the calcium chloride solutions are flushed out of the system and discharged by means of the pump 2G to the sewer. Water is then added to the system to fill the trays E i and the reservoir 56 up to the overflow it. Steam or preferably hot water from a heater (not shown) is circulated through radiators 33, 32 and ii in this order, and the hot water preferably permitted to return to the heater. The humidifying water, heated by exchanger H, is recirculated over the trays it by means of pump 20 and humidifies the air passing in contact with this water. The humidified air then passes in series through the heat exchangers 32 and 33 whereby it is always superheated and its relative humidity greatly reduced. This is advantageous in that the air so heated is less likely to condense out free moisture when it emerges from the outlet l0 and mixes with colder air or strikes cold surfaces.

Water is added in a small continuous stream to the recirculated humidifying water by means of a pipe 48 connected to the water supply so that at all times there will be a small excess of water overflowing at 68 so that the salts normally present in city water are held in solution and discharged to waste rather than separating out as scale upon the heating surfaces of radiator ill. If the heating water to be passed internally through the radiator H is of such a character that a deposit of low heat transferring properties is likely to be formed, an additional radiator entirely outside the housing may be substituted for radiator i'i,

When. air is humidified by contact with warm water, the air is either saturated with moisture or closely approaches saturation, and may even be supersaturated by the entrainment of droplets in the air stream. When air of this composition is discharged through ducts, condensation and dripping will occur with only a slight drop in temperature, creating a nuisance, or when discharged into a room whose air is of lower temperature a mist will be formed, or when the moisture laden air stream impinges on cold outside wall surfaces,

moisture will be deposited thereon. By providing for a positive increase in temperature of the air after humidification, I prevent these objectionable results.

This humidification and heating of the air I accomplish by circulating the hot Water from a steam boiler, or a hot water house heater, or from a water heating coil in a warm air furnace, first through the heat exchangers 33 and 532 and then through the means for heating the recirculated humidifying water, that is heat exchanger W. In this way the hot water is lowered in temperature during'its passage through the heat exchangers 33 and 32, thereby positively preventing the air during the humidifying step from being as hot as the air passing through these heat exchangers. In most installations, I may rely upon the thermal circulation of this hot water but if the stream is too sluggish or the apparatus at an improper level, I may correct this by means of a small circulating pump.

This provision for using hot water makes my apparatus adaptable as an accessory of any common central house heating equipment. For example, it provides for dependable and controllable air humidification even with an' oil burning steam .10 The use of a pump for recirculating cooled calcium chloride solution in the predrying step while drying air and for recirculating hot water for moistening air constitutes an improvement from another standpoint. Houses are frequently sup- 15 plied with sewer connections above the cellar floor level and in such cases the apparatus would have to be raised above the sewer connection so that the spent calcium chloride solution or the waste water could be discharged by gravity thereto. By providing a pump ,for recirculation, I am also able to discharge these liquids to any level necessary for their disposal.

Referring now to Fig. 3 of the accompanying drawings I show a form of apparatus whose parts 25 are identical with those in Figs. 1 and 2 with the exception of the arrangement of parts in compartment section 3 and bin section 4. The bottom plate 26a of this modified compartment section has its air passageway 21a across the ce'nter of its length rather than across the left hand end as shown in Fig. 1. The predryed air passes through this passageway and splits into two portions to pass in a right and left hand direction. The air stream to the left passes through a screen 35 Ma and thence in sequence through compartments 28a, 29a and 30a, the heat exchangers 32a and 33a and the screen 34a to the air outlet Illa. Similarly the air stream .to the right. passes through screen 3"), then through 28b, 32b, 29b,

40 33b, 30b and 34b to outlet lob. The discharged air may be delivered from outlets Illa and lb to various parts of the space to be conditioned or may be joined together in a single discharge duct outside the apparatus. The bins 31a, 38a and 45 39a and 38b and 3% may be constructed on a principle similar to the bins in Fig. 1. The rest of the parts of the apparatus are numbered the same as those shown in Figs. 1 and-2 and have the same functions.

50 Referring now to Fig. 4 of the accompanying drawings, I show another form of apparatus whose parts are identical with those in Figs. 1 and 2 except that the section containing the trays is a chamber A separate from the chamber 55 B containing the five compartments 28c, 29c, 39c, 30d and. 306, bins 310, 38c, 39c, 39d and 39c, and heat exchangers 32b, 33b, 33c and 33d. This arrangement has certain advantages especially in the construction of large equipment for treating 60 air for industrial purposes. By this division into two chambers an intermediate fan 49 in series between the chambers may be used to produce the air flow.

In this event the fan 49 draws air from cham- 65 her A and discharges it through duct 50 into chamber B as indicated. The pump 20 discharges the circulating liquid to the top tray in chamber A and the liquid after being cooled by the heat exchanger ll returns by gravity to the 70 bottom of chamber B through pipe where it mixes with the liquid draining from the compartments in chamber B and is again drawn to the pump through pipe 22. By means of liquid recirculation, this type of structure is made 75 operative. I moreover show at 52 a heat exchanger in the inlet duct 9 whereby the air may be heated or cooled before coming into contact with the recirculating liquid in chamber A.

In this form of the invention, the tendency of the calcium chloride to cake and clog in and around the outlets 36 in the bottom of the screen- 1 like support 26a upon which the calcium chloride rests is materially lessened. This tendency of the concentrated material to cool and resolidify in outlets 36 is lessened since the air issuing from the duct 50 is confined to contact with the solid material and does not pass directly above the surface of the solution in the bottom of the chamber B. Also because the concentrated solution which drips through the apertures 36 is dropped into and washed by the dilute solution issuing from the reservoir in the chamber A, there is no opportunity for resolidification due to cooling of the supersaturated solution below the temperature at which it solidifies.

It is to be understood that when the apparatus is operating as a dehumidifier in summer, solid calcium chloride is contained in compartments 28c, 29c, 30c, 30d and 30c and calcium chloride solution is recirculated by pump 20. During this operation it-may be advantageous to cool the incoming air below the atmospheric temperature by means of the heat exchanger 52. Moreover, when operating in winter as a humidifier the compartments 28c, 29c, 30c, 30d and 30e are empty and warm water is recirculated by the pump 20. At this period of the year it may be desirable to preheat the incoming air above the atmospheric temperature by means of the heat exchanger 52. This heat exchanger may be heated or cooled by passing therethrough any convenient fluid of the proper temperature to obtai the results desired.

It will be understood that with all these forms of apparatus, automatic control of the conditioned air in the house space may be provided by.

employing available control accessories such as ,humidistats, aquastats, and thermostats to actuspecific examples described are merely illustrations and I do not intended them to limit the scope of my invention.

By the term calcium chloride, as used in the appended claims, I intend to include either anhydrous calciumchloride or other solid varieties of calcium chloride containing water of crystallization. For general use I prefer solid calcium chloride containing about 25% of water of crystallization.

This application is a continuation in part of my copending application Serial No. 629,121, filed August '17,, 1932, Patent No. 2,026,935, dated January 7, 1936 and is also a division of my copending application Serial No. 672,415, filed May 23, 1933, Patent No. 2,026,936 dated January 7,

' I claim:

1. In an apparatus of the characte described, the combination of a chamber containing a plurality of vertically spaced intercommunicating shelves, means for circulating water in a closed circuit in contact with a water heater, thence to the series of said vertically spaced shelves, thence down from shelf to shelf and thenceinto contact with said water heater, means for adding water to said chamber, means for withdrawing water form 2. The process of humidifying air which com prises continuously recirculating a body of water in indirect heat transferring relationship with a heating fluid and in a succession of pools in direct contact with air to be humidified and thereafter passing said air into indirect heat transferring relationship with said heating fluid while circulating said heating fluid so that it comes into indirect heat transferring relationship first with the humidified air and thereafter with said recirculating water.

3. The process of humidifying air which comprises continuously recirculating a body of water 4. The process of partially saturating air with moisture which comprises'continuously circulating a heating fluid successively through an air heater and a water heater, continuously recirculating water in indirect heat exchanging relation with said heating fluid in said water heater, causing said water to be converted into spray form and passing the air to be partially humidifled successively through said water spray and through said air heater.

CHARLES R. DOWN S. 

